In 1987, Gray and Putzolo presented the five-minute rule, which was reviewed
and renewed ten years later in 1997. With the advent of flash memory in the
gap between traditional RAM main memory and traditional disk systems, the
five-minute rule now applies to large pages appropriate for today's disks and
their fast transfer bandwidths, and it also applies to flash disks holding
small pages appropriate for their fast access latency.
Flash memory fills the gap between RAM and disks in terms of many metrics:
acquisition cost, access latency, transfer bandwidth, spatial density,
and power consumption. Thus, within a few years, flash memory will likely
be used heavily in operating systems, file systems, and database systems.
The basic software architectures for exploiting flash in these systems are
called "extended buffer pool" and "extended disk" here. Based on the
characteristics of these software architectures, an argument is presented
why operating systems and file systems on one hand and database systems on
the other hand will best benefit from flash memory by employing different
software architectures.